I released WordPress theme “Stone Age” which was responsive w/o CSS media queries.
The technique was based entirely on floats, meaning that when the monitor got smaller, the right-hand columns simply folded under each other because there was no clearing.
We weren’t using CSS media queries back then and there weren’t any smartphones and tablets that we wanted to adapt our websites for. But responsive web design was already an issue back then because of the different monitor sizes that existed at the time.